Net-shape ceramic manufacturing as an aid to realize ultrasonic transducers for high-resolution medical imaging

High frequency ultrasonic transducers are in demand for medical imaging procedures requiring high spatial resolution. However, cost-effective fabrication for frequencies above approximately 20 MHz is challenging. One of the problems is the need for a thin layer of piezoelectric material. This is difficult because typical thick and thin film processes produce material which is too thin and lapping bulk materials is expensive and inefficient. In this paper, net shape ceramic processing is reported as an alternative. This can be achieved with viscous polymer processing followed by calendering of the green state material to produce thin sheets which can be dried, sintered and then cut to shape. Although such thin specimens are fragile, the addition of a supportive acoustic backing material allows straightforward processing into the final ultrasonic transducer. Here, piezoceramic made with TRS600FG material is reported, finished to thicknesses of 50 µm and 110 µm. The behaviour of these samples has been found to be similar to bulk material, for example with a thickness mode coupling coefficient, kT, of 0.52 and relative permittivity, eR S , of 1540. Prototype ultrasonic transducers with element diameters of a few millimetres have been made and operated at frequencies approaching 50 MHz. Testing has been performed underwater and the successful results suggest that net shape ceramic manufacturing is compatible with the fabrication of high frequency ultrasonic transducers.